A promoter is a DNA sequence which flanks a transcribed gene, and to which RNA polymerase must bind if it is to transcribe the flanking gene into messenger RNA. A promoter may consist of a number of different regulatory elements which affect a structural gene operationally associated with the promoter in different ways. For example, a regulatory gene may enhance or repress expression of an associated structural gene, subject that gene to developmental regulation, or contribute to the tissue-specific regulation of that gene. Modifications to promoters can make possible optional patterns of gene expression, using recombinant DNA procedures. See, e.g., Old and Primrose, Principles of Gene Manipulation (4th Ed., 1989).
U.S. Pat. No. 5,459,252 to Conkling and Yamamoto describes a root specific promoter designated RB7, which was identified in tobacco. U.S. Pat. No. 5,837,876 to Conkling et al. describes a root cortex specific gene promoter designated the RD2 promoter, which was also identified in tobacco.
Rather than use a promoter that is constitutively active, it is desirable to have promoters that are responsive to particular stimuli. In particular, if a promoter is responsive to a particular pathogen, then that promoter could be used to impart selective disease resistance to that pathogen through expression of a transgene that disrupts that pathogen.
U.S. Pat. No. 5,750,386 to Conkling, Opperman and Taylor describes pathogen resistant transgenic plants in which a nematode-responsive element is operatively associated with a nucleotide of interest (in this case, a gene encoding a product toxic to plant cells). One nematode responsive element was a deletion fragment of the RB7 root specific promoter described above.
U.S. Pat. No. 5,589,622 to Gurr et al. suggests nematode resistant transgenic plants in which cells of the plant contain a heterologous construct comprising a nematode responsive promoter operatively associated with a product disruptive of nematode attack. However, the DNAs disclosed by Gurr et al. as nematode responsive promoters do not appear to represent such promoters, and instead appear to represent extraneous or irrelevant DNA.
To impart useful traits to plants by the expression of foreign genes using genetic engineering techniques, a variety of pathogen-responsive promoters will be required to allow traits to be expressed selectively, in the appropriate plant tissues, and at the appropriate times. Accordingly, there is a continued need for pathogen responsive elements that operate in plant cells.